A Study of the Effects of Grain Size, Sheet Thickness and Punch Radii on Springback in Copper Sheets

Sheet metal forming is one of the most common manufacturing processes in the production of many mechanical components and auto parts. Therefore, accurate investigation of the effects of important parameters in the sheet metal forming process is of primary importance for engineers and designers. In the present study, the effects of grain size, punch radii, and sheet thickness on the springback in the W-shaped bending dies are evaluated. The investigated metal sheets are composed of pure copper with three thicknesses of 0.1, 0.3, and 0.5 mm. In this research, the annealing heat treatment process is conducted for 60 minutes at 500, 750, and 900 degrees on the Celsius scale to study the grain size in copper specimens, then the recovery process is performed at ambient temperature. The experimental results revealed that the rise of annealing temperature results in the significant variations of metallographic structure and grain size. According to the results, for a constant thickness, the mechanical properties changed by increasing the annealing temperature. As the grain size increased, the elongation and yield strength decreased. With a constant annealing temperature, the yield strength and elongation fell with a decrease in thickness. However, in both cases Young’s modulus does not change much. The results also indicated that by increasing the thickness of the sheet under the same conditions of grain size, the springback angle decreased as well, so that the springback angle minimized through selecting the radii of 0.3 mm for the punch. Additionally, it was concluded that the springback angle can be minimized with a decrease in t/d ratio for a constant sheet thickness. Based on these results, a multiple-choice regression model has been employed that the average error of this model for springback prediction was 8.08%.